Tom Cruise only has to appear on screen nowadays and I need one of those adult pacifiers that was reportedly used on the pregnant Katie Holmes in childbirth. Something in those boyish chops triggers in me an involuntary yelp: part dismay, part teenybopper salute to his awesome star-quality. It is said that after so many years of absorbing the photons of attention, stars become somehow incandescent. Tom is positively radioactive. Every time a new M:I comes out, the perennially youthful star is shown looking the way he looked during the Reagan administration - without obviously having had work done - and I feel like suggesting a new movie version of Oscar Wilde's The Picture of Dorian Gray. Dorian would be played by Tom and the picture up in the attic would be played by the star's cousin and Bizarro World lookalike William Mapother.

Cruise has often been really good. Anyone who saw his fantastic turns in Paul Thomas Anderson's Magnolia or Michael Mann's Collateral, knows that patronising him isn't on. But somehow it's the dark roles which tap into his, erm, intense quality - that intense quality which evidently makes working with him so memorable. His formidable ex-publicist, Pat Kingsley, must have felt that somewhere along the line, someone had sent her tape saying: "Your mission, Pat, should you decide to accept it, is to make Tom Cruise look as if he isn't at all times barking mad."

Anyway, here we are again for a third jog around Mission Impossible track and it's turning into a very tired experience. JJ Abrams, the creator of TV's Lost and Alias, has been entrusted with the franchise as writer-director. The gadgetry has been scaled down, there are hardly any laptops, and not even all that many scenes showing the latex masks. Again, there are tall buildings on which Cruise, with cable and grapple-hook, disports himself like a demure, tiny, hairless King Kong. Once again, the spiky simplicity of Lalo Schifrin's theme tune is needlessly funked up and the plot turns into unforgivable gibberish.

Cruise's Ethan Hunt, small but perfectly formed operative with the Impossible Mission Force, has now taken a low-profile job training "field agents". He is engaged to be married to a feisty young doctor, played by Michelle Monaghan, who thinks that he works for the city traffic department - and on their engagement party he is called back to the fray by his superior officers, Billy Crudup and Laurence Fishburne, to take on an arms-dealing villain in the form of Philip Seymour Hoffman, who is charmless and unpleasant rather than charismatic.

The truly yucky thing Hoffman's baddie does is insert tiny timer-bombs into people's brains, by propelling them up their nostrils while they are asleep. One of these mini-bombs detonates inside the head of one of Tom's comely female agents and I didn't know where to look. It's impressive, in a cringingly embarrassing way. The unfortunate woman's head doesn't blow up; it's just that at the awful moment her face suddenly goes blank and corpse-like, and eyes bulge and look off in weird directions. And the horrible thing is that a clunking flash-forward scene placed at the top of the movie reveals that one of the these awful brain-bombs is going to be placed in Tom's head! Oh no! To think of that pulchritudinous face suddenly looking like Marty Feldman.

Cruise himself does what he does without giving grounds for a refund of the ticket price. There's a scene where he infiltrates the Vatican disguised as a priest and in his pert cassock and missal he looks about 15. Will M:I IV actually be a prequel, showing Ethan Hunt's teenage years, tackling bullies and jocks at his local high school? Tom Cruise might even play the role. Unless he decides he looks too young.